1. Field of the Invention
The present invention relates to a tank. More specifically, the present invention relates to improvement in a valve fastening structure in a high-pressure tank which is filled with hydrogen gas or the like.
2. Background of the Invention
For a high-pressure tank used to store hydrogen, or the like, a structure obtained by attaching a valve assembly (a component with an in-built high-pressure valve, and the like) to a mouthpiece provided on a tank opening of the tank main body is used. Furthermore, in attaching the valve assembly to the mouthpiece, a simple screw structure is often employed, in which a male screw section on the valve assembly is screwed together with a female screw section on the mouthpiece (see Patent Document 1, for example).    Patent Document 1: Japanese Patent Application Laid-open No. 2007-263290
However, in a screw structure for a high-pressure tank as described above, there is a problem in that the strength of the screw section declines with repeated use.